Electron tube frequency multiplier of the traveling wave type



April 25, 1961 s. E. WEBBER ELECTRON TUBE FREQUENCY MULTIPLIER OF THE TRAVELING WAVE TYPE Filed Oct. 13, 1956 Invenfar Sfan/ey E Webber,

United States Patent ELECTRON TUBE FREQUENCY MULTIPLIER OF THE TRAVELING WAVE TYPE Stanley E. Webber, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Oct. 18, 1956, Ser. No. 616,859

4 Claims. (Cl. 328-49) The present invention relates to a frequency multiplier of the type employing an electrical discharge device having an extended interaction structure for interaction within an electron beam.

There has been a need for frequency multiplying electric discharge devices and it is particularly desirable that these devices also produce useable gain at the sametime that the frequency multiplying action takes place. In accordance with my invention, this combination of desirable characteristics is produced in a relatively simple electric discharge device system. Accordingly, it is an important object of the present invention to provide this simple electric discharge device system of the traveling wave type for producing frequency multiplication and amplification.

Further objects and advantages of my invention will become apparent as the following description proceeds, reference being had to the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is an elevational view in section, showing an electric discharge device system by my invention, and

Fig. 2 is a plan view in section of a portion of the system shown in Fig. l.

Referring now to the drawings, -I have illustrated my invention embodied in an electric discharge device system, including a traveling wave type of electric discharge device, including a generally cylindrical metal envelope 1, having a hemispherical closure 2 at one end of glass or similar insulating material and within which is mounted an electron gun, including a generally cylindrical cathode having a planar emitting surface 3 and a heater element 4. The gun also includes an accelerating electrode 5 in the form of an apertured annular disc and a control grid 6 interposed between the cathode surface and the accelerating electrode 5.

At the opposite end of the envelope 1 is a dlsk-hke collector electrode 7 supported from the end of the envelope by means of a metal cap 8, supported from the envelope by an insulating bead 9. Interposed between accelerating electrode 5 and the collector electrode 7 1s a slow wave structure, specifically a helix 10. The input and output ends of the helix terminate in conductors 11 and 12 which extend radially through circular openings in the metal envelope 1 and provide the inner conductors of concentric transmission lines sections which are completed by outer cylindrical conductors 13 and 14 respectively. The inner conductors 11 and 12 are supported from the outer conductors 13 and 14 by means of insulating beads 15 which also serve to seal hermetically the envelope. Concentric transmission line comprising conductors 12 and 14 provides the output line of the device. A small portion of the energy delivered to this output transmission line is fed back to an input transmission line section including conductors 11 and 13 by a circuit including a cavity resonator 16. As illustrated, this resonator is of generally cylindrical shape and is coupled to the input transmission line section by a coupling loop 17 forming an extension of the inner conductor 11. It is also coupled to derive a portion of the output energy by means of an inner conductor of a concentric transmission line, including a coupling loop 18 coupled to the resonator and a probe or capacity coupling 19 spaced closely adjacent the inner conductor 12 of the output line. The resonator 16 is resonant at the harmonic of the input frequency at which itis desired to operate the traveling wave tube and the length of the transmission line sections coupling the resonator to the input and output ends of the helix 10 are chosen so that the circuit is regenerative. As well understood by those skilled in the art, this means that the electrical length of the complete path including the helix 10 and the feed-back loop should be an integral multiple of 360 electrical degrees. The amount of energy fed back from the output circuit is relatively small and is dependent on the gain of the tube. For example, if the gain of the system is ten decibelsthen the feedback would be less than ten percent and is determined by the character of the coupling to the output circuit.

A suitable source of direct circuit voltage for operation of the device is provided by a battery 20, the negative terminal of which is connected to the cathode 3. Accelerating electrode 5 which is connected to an adjustable point on the battery by means of a slider 21 and is preferably operated at substantially the full positive voltage of the battery. The collecting electrode is connected to the positive terminal of the battery. As illustrated the helix, collector and envelope are all maintained at ground potential.

A source of signal voltage for modulating the electron beam is applied to the control grid 6 by means of any suitable signal source illustrated schematically at 22. The cathode 3, accelerating electrode 5 and control grid 6 provide a triode electron gun for producing a beam of electrons accelerated in accordance with the direct current voltage applied to the accelerating electrode 5 and amplitude modulated in accordance with the alternating signal voltage impressed between the cathode and the control grid 6.

In the operation of the system described, the control grid or any other suitable modulating means such as an lnput gap drift tunnel of the klystron type, is energized by a source of voltage of one frequency. As is usual in an ordinary thermionic cathode source, the beam contains a substantial percentage of harmonics. .In order to operate the device as a frequency multiplier and at the same time obtain amplification, the helix 10 is adapted to operate at a harmonic of the input frequency. This involves, as is well known, a correlation of the geometry of the slow wave structure, specifically of the pitch and diameterof the helix, with the direct current operating voltage and the desired operating frequency. While it is possible to accomplish this for low order of harmonics simply by operating the tube in the dispersive region (that is, a region in which the wave velocity along the helix varies substantially with frequency), it is possible to operate at much higher order harmonics by providing a feed-back loop including a resonant structure such as the resonator 16. In feeding back a small amount of the energy from the output circuit through this resonator which is tuned to the harmonic at which operation is desired, the length of the coupling transmission lines are such that this circuit as a whole is regenerative. In this manner, energy supplied to the output circuit, shown in the drawing as a concentric transmission line including conductors 12 and 14, may be amplified as compared to the input signal and is a harmonic of the input frequency. The tendency of the helix to oscillate may be minimized by the application of an attenuator in the form of a high loss Patented Apr. 25, 1 961 While I have described a particular embodiment of my; invention, it will be apparent to those skilled, in the art that changes and modifications may be made without departing from my invention in its broader aspects and I aim, therefore, in the. appended" claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim asnew and desire to secure by Letters Patent of the United States is:

1. An electron beam discharge device frequency multiplying system comprising electrode means establishing an elongated electron beam and accelerating it to a predetermined constant average velocity along a predetermined path including means for modulating said beam at a predetermined frequency, a conductive slow wave structure extending along said beam path in energy exchanging relation with a beam passing along said path, a feed-back circuit coupled between. the output and input ends of said slow wave structure. andproviding a regenerative feedback of energy at a frequency which. is a multiple of said'predetermined frequency and includinga circuit tuned to said multiple of said predetermined frequency.

2. An electron beam discharge device frequency multiplying system comprising electrode means establishing an elongated electron beam and accelerating it to a predetermined constant average velocity along a predetermined path including means for modulating said beam at a predetermined frequency, a helical slow wave structure extending along said beam path in energy exchangingrelation with a beam passing along said path, a feed-back circuit coupled between the output and input ends' of said helical slowwave structure and providing a regenerative'feedback of energy ata frequency which is a multiple of said predetermined frequency and including a cavity resonator tuned to said multiple of said predetermined, frequency.

3. An electron beam discharge-device frequency multiplying system comprising electrode means establishing an elongated electron beam and accelerating it to a predetermined constant average velocity along a predetermined path including means for modulating said beam at a predetermined frequency, a helical slow wave structure extending along said beam path in energy exchanging relation with a beam passing along said path, an output circuit for supplying energy to a load at a frequency which is a multiple of said predetermined frequency, a feed-back circuit coupled between said output circuit and the input end of said slow wave structure and providing a regenerative feedback of energy at a frequency which is a multiple of said predetermined frequency and including a circuit tuned to said multiple of said predetermined frequency.

4. An electron beam discharge device frequency multiplying system comprising electrode means establishing an elongated electron beam and accelerating it to a predetermined constant average velocity along a predetermined path including in the order named, means for modulating.

said beam at a predetermined frequency, a helical slow wave structure extending along. said beam path in energy exchanging relation with a beam passing along said path, and-a collecting electrode, the pitch and diameter of said helical slow wave structure and the average velocity of said beam being correlated for operation at a second frequency which is a multiple of said predetermined frequency, a feed-back circuit coupled between the output and input ends of said slow wave structure and providing; a regenerative feedback of energy at said second frequency and including a distributed circuit resonant at said second frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,603,773 Field July 15, 1952 2,724,775 Field Nov. 22, 1955 2,751,518 Pierce June 19, 1956 2,774,869 Burke. Dec. 18, 1956 FOREIGN PATENTS 629,238 Great Britain Sept. 15', 1949 

